Allen-Bradley vs Siemens PLCs

The Allen-Bradley Logix family is the most popular programmable logic controller (PLC) series in the United States, consisting of multiple variants. For this comparison, we’ll focus on the ControlLogix, CompactLogix, and MicroLogix PLCs.In contrast, Siemens dominates the European market with its SIMATIC PLCs, which are widely used across industries. The Siemens counterparts to the Allen-Bradley Logix family include the S7-200, S7-300, and S7-400 controllers.

General Differences: Allen-Bradley vs Siemens

When it comes to performance, both Allen-Bradley and Siemens PLCs deliver similar speeds and reliability, with comparable output capabilities. However, the main difference lies in how easily they integrate into control systems and how user-friendly they are. 

In terms of hardware installation, Allen-Bradley PLCs require both a proprietary rack and power supply. Siemens offers more flexibility in this regard, as their PLCs can be powered by any 24V DC power supply and do not require a specific rack for installation.

PLC Programming is another area where Allen-Bradley has an edge. Its PLC controllers are easier to learn and more intuitive, making it suitable for less experienced users. On the other hand, Siemens PLCs are more complex and typically require advanced PLC programming skills, making them better suited to highly trained professionals.

The communication protocols also reveal differences that align with their geographic strongholds. Allen-Bradley PLCs support North American protocols such as DeviceNet, ControlNet, Ethernet/IP, DH+, and DH485. Siemens, being more popular in Europe, predominantly uses European protocols such as Profibus, ASI, and MODBUS TCP/IP.

Unit-Specific Comparisons

ControlLogix vs S7-400

Both the Allen-Bradley ControlLogix and Siemens S7-400 are designed for large-scale industrial automation systems and offer significant modularity and expandability. Introduced in 1999, the ControlLogix series is a workhorse in the automation industry, offering a range of models such as the 5580 and 5570. Siemens’ S7-400, in comparison, features models like the CPU 412, CPU 414, and CPU 417, which also cater to large automation environments.

When comparing memory, ControlLogix provides up to 20 MB of user memory in its high-end models, while Siemens S7-400’s split memory architecture, with separate main and load memory, enhances performance.

In terms of I/O capabilities, both systems support extensive distributed I/O, capable of handling thousands of I/O points. ControlLogix’s chassis-based modularity allows for greater customization, while the S7-400, though modular, can only accept up to 21 expansions. Both controllers, however, support a combination of analog and digital I/O expansion, ensuring versatility in a wide range of applications.

Communication methods show a clear advantage for ControlLogix, which supports EtherNet/IP, ControlNet, DeviceNet, DH+, and USB client connections. In contrast, the S7-400 mainly relies on PROFIBUS and Ethernet, the latter primarily for industrial automation communication rather than broader networking.

For safety features, both Allen-Bradley and Siemens offer embedded safety modules. Allen-Bradley’s GuardLogix controllers provide comprehensive safety control for various safety-approved applications, while Siemens’ S7-400 has now integrated safety features similar to those in the GuardLogix line.

CompactLogix vs S7-300

The Allen-Bradley CompactLogix and Siemens S7-300 controllers are designed for small to medium-sized industrial automation projects. CompactLogix, available in both all-in-one and modular configurations, offers a flexible solution for a range of applications. Siemens’ S7-300 also delivers flexibility, with ten base models offering various sizes and communication port access.

Regarding memory, CompactLogix models offer between 0.6 MB and 10 MB of user memory, while the S7-300’s memory ranges from 32 KB in the lower-end CPU 312 to 2.56 MB in the high-end CPU 319-3 PN/DP.

Both PLC controllers excel in I/O modularity. CompactLogix is designed for distributed I/O, supporting multiple nodes and allowing significant system expansion. Its local I/O ranges from 8 to 31, with up to 250 nodes in the higher-end models. The S7-300, though modular, offers fewer expansions, supporting up to 1024 digital I/O and 256 analog I/O.

When it comes to communication, Siemens S7-300 provides a wider array of communication protocols, particularly European standards like Profibus and Profinet. CompactLogix, while somewhat more limited, still offers flexible communication options, including EtherNet/IP and DeviceNet.

MicroLogix vs S7-200

At the entry-level, the Allen-Bradley MicroLogix and Siemens S7-200 PLC controllers serve smaller, standalone applications with basic control and motion functions. Both families consist of five base models. For Allen-Bradley, these include the MicroLogix 1000, 1100, 1200, 1400, and 1500, while Siemens offers the CPU 221, 222, 224, 224XP, and 226.

In terms of memory, the MicroLogix family provides up to 10K user memory, whereas Siemens S7-200 reaches 16K in its higher-end models. Siemens also includes data logging memory and battery backup in all models, while only certain MicroLogix models offer these features.

The MicroLogix family generally provides more digital I/O capabilities than the S7-200. For instance, the MicroLogix 1400 offers up to 32 I/O points, while Siemens’ S7-200 ranges from 6 inputs and 4 outputs on the CPU 221 to 24 inputs and 16 outputs on the CPU 226.

Analog I/O capabilities are also superior in the MicroLogix family, where up to 256 expansion modules can be added in some models. Siemens’ S7-200 offers more limited analog expansion through external modules.

For pulse outputs, both brands are comparable, offering 2 pulse outputs per controller, though Siemens’ CPU 224XP offers a higher frequency output at 100 kHz. Additionally, most Allen-Bradley MicroLogix controllers include an embedded real-time clock, a feature only found in certain Siemens models.

Communication flexibility is another area where Allen-Bradley surpasses Siemens. MicroLogix controllers support multiple protocols, including RS-232, Ethernet/IP, and Modbus TCP/IP, providing greater adaptability. Siemens’ S7-200, in contrast, primarily offers RS-485 and Profibus communication.

Conclusion: Choosing the Right PLC

When deciding between Allen-Bradley and Siemens PLC controllers, the best choice depends largely on your region, system requirements, and available expertise. Allen-Bradley is the preferred option for those who value ease of PLC programming, quick troubleshooting, and extensive support for North American industrial automation companies. In contrast, Siemens offers powerful, complex solutions that integrate well with European industrial systems and provide a greater range of communication options and memory flexibility. Both brands are leaders in the automation industry, and the decision ultimately comes down to your specific needs for performance, integration, and expandability.At Mizen Automation we can help you find the PLC you are looking for, contact our expert sales team today.